According to the Wiki on I have STPC your booking will be cancelled and in typical QR fashion they will not usually tell you until to try to check-in at the stpc desk at DOH.
" 6) The Hotel Accommodation is provided only when the connection time is between 8 and 24 hours at Doha. If there is a change in the Flight Schedule (either triggered by the airline or by the guest) and the new connection time in Doha becomes less than 8 hours or more than 24 hours then the existing Hotel Confirmation will become invalid. "
Please remember to read "new connection time" as "new SHORTEST connection time" That being the intent of QRs poorly worded document as several members have already documented in the QR STPC stopover policy thread..